[TUHS] PDP-8 (was: 2.11BSD cross compiler)
Greg 'groggy' Lehey
grog at lemis.com
Thu Sep 30 14:22:29 AEST 2010
On Tuesday, 28 September 2010 at 22:59:22 -0400, John Cowan wrote:
> On Tue, Sep 28, 2010 at 10:38 PM, Larry McVoy <lm at bitmover.com> wrote:
>> Color me old school. I like MIPS, I worked at SGI (got married to
>> an old school MIPS gal) but PDP-11 is so frigging intuitive. How
>> can you not understand that instruction set? If you can't, well,
>> sorry, not so much in my book. It's like a stripped down C.
> Yeah. I used it on and off, but my serious assembler programming
> was on the PDP-8. Now *that* was seriously small, but you had to
> know the tricks, like how to find out the absolute address of the
> 128-word memory page following the one you are on when writing PIC
> code for OS/8 device drivers, or how to microprogram the operate
> instructions get interesting constants into the AC.
That was my first machine too (well, a PDP-12, which was really a
hybrid PDP-8/LINC-8, but I only used the PDP-8 instructions). That
was a nice, compact instruction set. It has the great advantage that
I can still remember just about every instruction today. Remember the
autoincrement registers? Even in those days they looked like a
kludge, but they helped a lot.
>> Come on - has anyone ever seen a better instruction set? More
>> complicated, yeah, holy moly, yeah. But cleaner? We owe DEC
>> for that one.
> I remember how appalled I was when I saw the VAX instruction set.
> Luckily, it didn't matter: I never did assembler again. Still,
> trying to make people think in octal at this late date seems
It's funny how long octal clung on. It should have gone away with 8
bit bytes. But somehow I still have a soft spot for octal, and
numbers like 7778 still look wrong.
>> Personally, I like anyone who can do any assembler. One of my interview
>> questions is "have you written swtch?"
>> If you don't get the question you are not an OS person,
>> if you are, of course you get it.
Hmm. Am I expected to understand this? Seriously, I don't know how
many people really wrote anything like swtch ().
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